JP4738621B2 - Pulse detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pulse detection device using a piezoelectric element.
[0002]
[Prior art]
Biological veins contain important information for diagnosing diseases. Recently, in medical facilities such as hospitals, a portable pulse detector is attached to the patient's arm and transmitted from the portable pulse detector. A system for receiving the detected pulse detection data of the patient at the hospital side and grasping the state of the patient has been studied. Piezoelectric elements are effective for reducing the size and weight of pulse detectors, and development of pulse detectors using piezoelectric elements is being promoted, considering application to the above-described system.
[0003]
FIG. 11 shows a pulse detecting device 100 using a conventional piezoelectric element. As shown in FIG. 11, the pulse detecting device 100 is obtained by embedding and fixing two piezoelectric elements 110 and 120 in a resin 130 (or gel). Here, metallic electrodes are formed on both surfaces of the piezoelectric elements 110 and 120 in the thickness direction (not shown). In addition, a drive voltage application probe (terminal, lead wire, etc.) is connected to both electrodes of the piezoelectric element 110, and a voltage signal output probe (not shown) is connected to the upper and lower electrodes of the piezoelectric element 120. The
[0004]
The patient's pulse is detected by using the pulse detection device 100 at the time of medical examination. Specifically, when a driving voltage is applied to both electrodes of the piezoelectric element 110, the piezoelectric element 110 is excited to generate ultrasonic waves, and the ultrasonic waves are transmitted into the living body via the resin 130. The ultrasonic wave transmitted into the living body is reflected by the blood flow of the living body, and the reflected ultrasonic wave is received by the piezoelectric element 120 through the resin 130.
[0005]
At this time, a frequency change occurs in the ultrasonic wave transmitted by the piezoelectric element 110 and the ultrasonic wave received by the piezoelectric element 120 due to the Doppler effect of blood flow. Further, since the blood flow velocity changes in synchronization with the pulse, the pulse of the living body is detected by the change in the frequency of the ultrasonic wave.
[0006]
The frequency change due to the Doppler effect is expressed by Equation 1. In order to effectively extract the Doppler effect from Equation 1, that is, increase the frequency change, the piezoelectric elements 110 and 120 are inclined with respect to the living body surface and blood flow.
[0007]
f1 = 2 × v (t) × cos θ × f0 / c (1)
(F0: original frequency, v (t): blood flow velocity, c: speed of sound in the living body, f1: frequency after Doppler change, θ: angle between blood flow and piezoelectric element)
[0008]
[Problems to be solved by the invention]
In the conventional detection method, the piezoelectric element is tilted in order to increase the Doppler effect. However, considering the reflection of the ultrasonic wave, the ultrasonic wave transmitted into the living body is reflected by the blood flow of the living body as shown in FIG. However, considering the direction of reflection, most of the light does not go to the receiving piezoelectric element as indicated by the arrow in FIG. Therefore, in order to obtain an output exceeding a certain level, a larger amount of power is required at the time of input. Therefore, the present invention provides a pulse detection device that transmits ultrasonic waves that are focused in a living body and can obtain more output with less input voltage, and a method for manufacturing the same. Moreover, although the distance from the biological surface to the blood vessel changes depending on individual differences and measurement locations, a pulse detection device that can cope with the change is provided.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a pulse detection device provided by the present invention will be described.
[0010]
The measurement unit of the pulse detection device provided by the present invention is arranged on a blood vessel. The measuring unit is mainly composed of a transmitting piezoelectric substrate and a receiving piezoelectric substrate, and concentric interdigital electrodes are arranged on the surface of the transmitting piezoelectric substrate. By inputting a high-frequency electric signal to the interdigital electrode, a leaky Lamb wave is excited in the transmitting piezoelectric substrate. The excited Lamb waves emit ultrasonic waves into the living body through the resin layer. At this time, the ultrasonic wave is focused in the living body by the concentric interdigital transducer. The ultrasonic wave emitted into the living body is reflected by the blood vessel in the living body and reaches the receiving piezoelectric substrate. At this time, since the blood vessels in the living body pulsate in synchronization with the heartbeat, the time from when the ultrasonic wave is transmitted until it is received varies. By detecting this change, the pulse can be detected. Since the ultrasonic wave is reflected also in the blood flow in the blood vessel, the Doppler effect can be used as usual.
[0011]
The place to be focused in the living body can be controlled by the period length of the interdigital electrode and the frequency of the input signal. When the input frequency is constant, the focus point of the ultrasonic wave changes by changing the period length of the interdigital electrode. Therefore, multiple focus points can be formed by forming multiple period lengths on the same transmission piezoelectric substrate. Will be able to. Thereby, it is possible to cope with a change in the distance from the surface of the living body to the blood vessel position due to individual differences and measurement locations such as the head, arms, and feet.
[0012]
In addition, since the acoustic impedance is too different between the piezoelectric substrate and the living body in order to make the ultrasonic wave enter the living body, the ultrasonic wave is reflected as it is, so by providing a resin layer on the piezoelectric substrate, the ultrasonic wave is reflected. To be easily incident. Furthermore, a resin having high adhesion to a living body is formed, and an air layer in which ultrasonic waves are attenuated between the measuring unit and the living body is eliminated as much as possible so that transmission and reception can be performed efficiently.
[0013]
Furthermore, the pulse detection device provided by the present invention is composed of a band on which a measurement unit, a circuit unit, a display unit, and a recording unit can be attached to a part of the body, and is therefore portable.
[0014]
As described above, in the present invention, a pulse detection device that detects a pulse by forming concentric interdigital electrodes on a transmission piezoelectric substrate and measuring the arrival time of a reflected wave is provided.
[0015]
According to this configuration, the ultrasonic wave can be focused and emitted on the blood vessel, and more output can be obtained with a smaller input voltage than in the conventional method. Furthermore, concentric interdigital electrodes on the piezoelectric substrate for transmission By having a plurality of period lengths, there are a plurality of focus points in the living body, and it is possible to provide a pulse detecting device that can cope with a change in the distance from the living body surface to the blood vessel.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The pulse detection device of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 shows the entire pulse detection device of the present invention and a mounting example. In FIG. 1, the pulse detection device 1 includes a display / recording unit 3, a measurement unit 4, and a band 5. The display / recording unit 3 and the measurement unit 4 are connected by a copper wire (not shown) in the band 5. The pulse detection device 1 is fixed to the living body 2 by a band 5.
[0018]
FIG. 2 shows a cross-sectional view when mounted. The pulse detecting device 1 is mounted on the living body 2 such that the measuring unit 4 comes on a blood vessel 21 such as a radial artery, ulnar artery, carotid artery, etc. in the living body. Fixed by. Therefore, the pulse detection device 1 can be always mounted and measured continuously. In FIG. 1, an arm is used as an example of the living body 2. If the measurement unit 4 can be mounted on the blood vessel 21, the place of the living body 2 can be changed to a foot, a neck, an upper arm, etc. Can be installed at any location.
[0019]
A block diagram of the display / recording unit 3 and the measuring unit 4 is shown in FIG. The measurement unit 4 includes a measurement unit 40 and a circuit unit 48, and the display / recording unit 3 includes a display unit 31 and a recording unit 32. The transmission piezoelectric substrate 41 of the measurement unit 40 is driven by the circuit unit 48 in the measurement unit 4. The receiving piezoelectric substrate 42 that receives the reflection from the living body converts the ultrasonic wave into an electric signal and transmits it to the circuit unit 48. The circuit unit 48 obtains the distance from the biological surface to the blood vessel from the time taken for transmission / reception. In addition, the movement of the blood vessel caused by the pulsation associated with the heartbeat is captured from the time difference between transmission and reception to obtain the pulse. The display / recording unit 3 receives these pieces of information, displays the measurement results on the display unit 31, and records them on the recording unit 32. The stored data can be displayed on the display unit 31 by calling the data stored in the recording unit 32 on the display unit 31. In addition, when the circuit unit 48 is configured to demodulate the frequency change caused by the Doppler effect, it is possible to measure blood flow and pulse from the frequency change.
[0020]
The relationship between the measurement unit 4 and the living body 2 is shown in FIG. Transmission and reception of ultrasonic waves will be described with reference to FIG. An ultrasonic wave is emitted into the living body 2 from the transmitting piezoelectric substrate 41 of the measuring unit 40 installed on the blood vessel 21, and the ultrasonic wave reflected by the blood vessel 21 reaches the receiving piezoelectric element.
[0021]
An interdigital electrode 43 is formed on the transmission piezoelectric substrate first surface 41 a of the transmission piezoelectric substrate 41, and a high frequency electrical signal is input from the circuit unit 48. At this time, the polarization direction is a direction perpendicular to the transmitting piezoelectric substrate first surface 41a. Further, when the thickness of the transmission piezoelectric substrate is d and the wavelength of the Lamb wave is λ, the transmission piezoelectric substrate first surface 41a and the transmission piezoelectric substrate second surface 42b are satisfied when d <λ is satisfied. Vibrates elastically. The elastic vibration generated on the transmitting piezoelectric substrate second surface 42 b is transmitted as an ultrasonic wave into the living body 2. The radiation angle φ transmitted to the living body 2 is expressed by Equation 2.
[0022]
sinφ = Vs / Vp (2)
(Φ: Radiation angle, Vp: Sound velocity in the piezoelectric element, Vs: Sound velocity in the living body)
The transmitted ultrasonic wave is reflected by the arterial blood vessel 21 in the living body 2 and reaches the receiving piezoelectric substrate second surface 42b. At this time, when the thickness of the receiving piezoelectric substrate is d and the wavelength of the Lamb wave is λ, the second surface 42b of the receiving piezoelectric substrate is an ultrasonic wave as in the case of the transmitting piezoelectric substrate when the condition of d <λ is satisfied. By hitting, it vibrates elastically and becomes an electric signal by the interdigital electrode 43 of the receiving piezoelectric substrate first surface 42a. At this time, the polarization direction of the piezoelectric substrate is a direction perpendicular to the receiving piezoelectric substrate first surface 42a. The electric signal is displayed and recorded by the display / recording unit 3 as described above through the circuit section 48 shown in FIG.
[0023]
The interdigital electrode pattern on the piezoelectric element shown in FIGS. 6 and 7 will be described. FIG. 6 shows a pattern in which the electrode periodic length is constant on the first surface 41 a of the transmitting piezoelectric substrate 41 and the first surface 42 a of the receiving piezoelectric substrate 42. At this time, as shown in FIG. 4, an ultrasonic wave focused on one place can be emitted into the living body. FIG. 7 shows a pattern including two electrode period lengths. In the case shown in FIG. 7, there are two in-vivo focus points as shown in FIG. The focus position can be designed with the radius r and period length l of the concentric interdigital electrodes and the frequency f of the input signal. Vp (Vp = l · f) is determined from the period length l and the frequency f of the input signal, the radiation angle φ is determined from Equation 2, and the focus position in the depth direction is determined from the radius r, so the focus position can be designed. It is. Although there are two types of cycle lengths in FIG. 7, a plurality of focus points can be formed by having a plurality of cycle lengths. Therefore, the ultrasonic wave can be focused on the blood vessel without being affected by the distance from the body surface to the blood vessel due to the measurement location or individual differences.
[0024]
Next, the measurement unit 40 will be described in detail with reference to FIG. The transmitting piezoelectric substrate 41 and the receiving piezoelectric substrate 42 are bonded by an adhesive resin 45, and a conductive resin 49 is applied on the adhesive resin 45. The conductive resin 49 is applied to cut a signal transmitted from the interdigital electrode 43 on the transmitting piezoelectric substrate 41 to the interdigital electrode 43 on the receiving piezoelectric substrate 42 in the air. Further, when the adhesive resin 45 is made by mixing an ultrasonic absorber with an adhesive, the propagation wave from the transmitting piezoelectric element 41 to the receiving piezoelectric element 42 via the adhesive resin 45 can be cut. The received signal processing is simplified. Further, the transmission piezoelectric substrate 41 and the reception piezoelectric substrate 42 are bonded to a support portion 44. The support portion 44 is preferably made of a metal such as brass or aluminum in order to remove electrical noise. Moreover, the intensity | strength with respect to the impact from the outside of the measurement part 40 increases by using metal.
[0025]
For the material of the interdigital electrode 43 on the first piezoelectric substrate surface 41a for transmission and the first piezoelectric substrate surface 42a for reception, a metal having a low electrical resistance, for example, pure aluminum is used. A two-layer structure of chromium and gold. Here, chromium is used to firmly bond gold and the piezoelectric element. When workability such as wire bonding is remarkably inferior in a subsequent process due to a metal compound of chromium and gold, nickel may be sandwiched between chromium and gold to form three layers of chromium, nickel, and gold.
[0026]
A matching resin 46 and a contact resin 47 are formed on the second piezoelectric substrate surface 41b and the second piezoelectric substrate surface 42b for reception. In order to efficiently transmit ultrasonic waves between the living body and each of the piezoelectric substrates 41 and 42, the matching resin 46 is provided, and the acoustic impedance of the matching resin 46 is set to the acoustic impedance Zl of the living body and the acoustic impedance Zc of the piezoelectric element. Must be between values. The acoustic impedance is a value indicating the ease of sound wave propagation, and the value varies depending on the Young's modulus and density. And in the measurement part 40 which has the structure shown in FIG. 9, the ideal acoustic impedance Zm of the matching resin 46 is
Zm = (Zc × Zl) ^1/2 (3)
Can be indicated by Substituting Zl = 1.5 M (N · sec / m ³ ) and Zc (using PZT) = 30 M (N · sec / m ³ ) into Equation ( ³ ), Zm = approximately 6. 7M (N · sec / m ³ ).
[0027]
Based on this calculated value, in this embodiment, an acrylic resin having an acoustic impedance of about 5.6 M (N · sec / m ³ ) is used for the matching resin 46.
Further, an adhesion resin 47 made of a silicon resin is formed on the alignment resin 46. This is to improve the adhesion of the measurement unit and the living body and further improve the propagation of ultrasonic waves. When the silicon resin is used for the adhesion resin 47, since the silicon resin is soft, the adhesion with the living body 2 is improved, and the air layer existing between the living body 2 and the measurement unit 40 can be reduced. It is possible to suppress the attenuation of ultrasonic vibration by the air layer. In addition, the silicon-based resin has good compatibility with a living body and has little influence even when it is brought into close contact with the skin. Thereby, reflection and attenuation of ultrasonic waves can be prevented.
[0028]
Next, the shapes of the transmitting piezoelectric substrate 41 and the receiving piezoelectric substrate 42 and the adhesive resin 45 will be described with reference to FIG. The adhesive resin 45 shown in FIG. 10 is bonded to the interdigital electrode 43 by cutting the transmitting piezoelectric element 41 and the receiving piezoelectric element 42 so as to be inclined. By doing so, the propagation wave from the interdigital electrode 43a on the transmitting piezoelectric substrate first surface 41a to the interdigital electrode 43b on the receiving piezoelectric substrate first surface 42a via the adhesive resin 45 is scattered, and the circuit unit 48 The received signal processing is simplified.
[0029]
【The invention's effect】
As described above, according to the pulse detection device of the present invention, signals and propagation waves that propagate in the air from the transmitting piezoelectric substrate to the receiving piezoelectric substrate can be removed, and ultrasonic waves can be focused and transmitted efficiently into the living body. Therefore, it is possible to provide a pulse detection device with improved blood vessel detection sensitivity.
[0030]
In addition, by adopting a structure that takes into account acoustic impedance and adhesion to a living body, attenuation of ultrasonic waves can be suppressed and ultrasonic waves can be propagated efficiently.
Furthermore, by providing a metal support for supporting the transmission / reception substrate, the strength against external impact is improved.
[0031]
Moreover, the pulse detecting device can be easily carried by providing a belt for mounting the pulse detecting device.
[Brief description of the drawings]
FIG. 1 is an example of an external view showing a state diagram in which a pulse detection device of the present invention is mounted on a living body.
FIG. 2 is a diagram showing a cross-sectional configuration of a pulse detection device according to the present invention.
FIG. 3 is a block diagram showing internal configurations and connection states of a display / recording unit and a measurement unit.
FIG. 4 is a diagram showing a cross-sectional configuration of a pulse detection device according to the present invention.
FIG. 5 is a diagram showing a state of a transmitting piezoelectric substrate and a receiving piezoelectric substrate.
FIG. 6 is an example showing a piezoelectric substrate, an interdigital electrode, and an adhesive portion.
FIG. 7 is an example showing a piezoelectric substrate, an interdigital electrode, and an adhesive portion.
FIG. 8 is a diagram showing a state of a transmitting piezoelectric substrate and a receiving piezoelectric substrate.
FIG. 9 is a cross-sectional view of a measurement unit.
FIG. 10 is an example showing a piezoelectric substrate, an interdigital electrode, and an adhesive portion.
FIG. 11 is a diagram showing a conventional example.
FIG. 12 is a diagram showing a cross-section of a conventional configuration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pulse detection apparatus 2 Living body 21 Blood vessel 3 Display / recording unit 31 Display part 32 Recording part 4 Measuring unit 40 Measuring part 41 Transmission piezoelectric substrate 41a Transmission piezoelectric substrate first surface 41b Transmission piezoelectric substrate second surface 42 Reception piezoelectric Substrate 42a Reception piezoelectric substrate first surface 42b Reception piezoelectric substrate second surface 43 Interdigital electrode 44 Support portion 45 Adhesive resin 46 Matching resin 47 Adhesive resin 48 Circuit portion 49 Conductive resin 5 Band 6 Fastener 100 Conventional pulse detection Device 110 Piezoelectric Element 120 Piezoelectric Element 130 Resin

Claims (4)

In a pulse detection device comprising a measurement unit, a circuit unit that drives the measurement unit, a display unit that displays measurement results, and a recording unit that records the measurement results,
The measurement unit is composed of a transmission piezoelectric substrate polarized in the thickness direction and a reception piezoelectric substrate polarized in the thickness direction,
Each of the transmitting piezoelectric substrate and the receiving piezoelectric substrate has first and second planes parallel to each other, and at least two types of interdigital electrodes for lamb wave excitation are provided on each of the first planes. Each of the interdigital electrodes is arc-shaped and formed to be concentric with each other ,
Between each of the interdigital electrodes, a conductive resin is provided over at least the width of the interdigital electrode ,
The pulse detecting device, wherein the conductive resin is applied to the first plane side of a material for bonding the transmitting piezoelectric substrate and the receiving piezoelectric substrate.   2. The pulse detecting device according to claim 1, wherein the second plane of the transmitting piezoelectric substrate and the receiving piezoelectric substrate is arranged in the same plane, and the second plane side is attached to a living body. . In any one of claims 1 or claim 2, pulse detector, characterized in that it comprises a resin layer on the second plane of the transmitting piezoelectric substrate and the piezoelectric substrate said receiving. In any one of claims 1 to 3, wherein the measuring unit and the circuit unit and the display unit and the recording unit, the pulse detection device, characterized in that attached to the band that can be attached to a portion of the body.

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